Sow discord where the upper ranks are arrogant and lower ranks are
resentful.

Where you see doubt in movement, create fear that leads to retreat.

Where officers do not respect the leader and want to go home, block off
the easy routes and lay ambush in the trickier ways.

When advance is easier for them than retreat, wait for them.

When retreat is easier than advance, push them back.

If they camp in wetlands, wait for rain and flood.

If they camp amongst trees or grasses, use fire.

If they camp for a long time, wait for them to be lax and then launch a
surprise attack.

Discussion

Understanding their leader can give great advantage. War is often more about
taking advantage of people and situations than executing previously-known plans.
Whenever you get new information, current plans should be reviewed in the light
of this, although do beware of constantly changing tack in ways that hinder
progress and confuse your troops.

Remember also that your enemy will also be assessing your leader and your
approaches in movement, attack, retreat and so on. This gives you opportunity to
lead them to think that you will likely do one thing when you can then act in
surprising ways that catch them off guard.